There are many cooling schemes for generator stator end windings. Most cooling schemes involve delivering cooling fluid to within a rotating rotor. The cooling fluid is used to cool windings within the rotor. The cooling fluid is then delivered to the stator end windings by means of an orifice or a simple radial passage located in the rotating rotor. Accordingly, as the rotor rotates, cooling fluid sprays from the rotor, bathing the stator end windings with cooling fluid.
U.S. Pat. No. 4,496,862, which issued on Jan. 29, 1985 to Weber and commonly assigned with the subject invention, although not directed to a stator end winding cooling scheme, nonetheless shows a typical prior art cooling scheme for stator end windings. Weber provides for generally radial passages, in alignment with end turns of a stator winding, extending from within a rotor to the periphery of the rotor. As a consequence of this construction, cooling fluid may be directed at such windings for cooling purposes.
During operation of a variable speed generator, it is desirable to maintain a steady flow of cooling fluid to the end windings. It is not desirable to have rates of flow of the fluid vary as a function of the rotor speed. Accordingly, the above-described cooling method works at its best when generator speed is constant. In fact, the generator disclosed in Weber operates at a constant speed in the preferred embodiment. If, using the Weber cooling scheme, the generator speed were to vary substantially, cooling fluid flow rates through the radial passages would vary substantially due to the widely varying fluid pressures within the rotor.
The generator within which the subject invention is intended to function normally operates at variable speeds. Accordingly, the above-described scheme of spraying stator end windings with an orifice or a simple radial passage would be inadequate to assure an unchanging rate of cooling fluid flow to the generator end windings.
Accordingly, no prior invention has ever addressed the problem of cooling stator end windings in a generator which operates at varying speeds, the object being to render rates of flow of cooling fluid to the end windings insensitive to generator rotor speed. The subject invention is the first to address the problem of variable cooling fluid flow rates within a generator operating at variable speed.